[composer] wrap UniversalClassLoader require in if class_exists

src/Composer/Autoload/AutoloadGenerator.php

@@ -42,7 +42,9 @@ class AutoloadGenerator
 <?php
 // autoload.php generated by composer
 
-require_once __DIR__.'/../vendor/symfony/symfony/src/Symfony/Component/ClassLoader/UniversalClassLoader.php';
+if (false === class_exists('Symfony\Component\ClassLoader\UniversalClassLoader', false)) {
+    require __DIR__.'/../vendor/symfony/symfony/src/Symfony/Component/ClassLoader/UniversalClassLoader.php';
+}
 
 use Symfony\Component\ClassLoader\UniversalClassLoader;